Taxonomy & naming
Betta midas was described by Tan Heok Hui in 2009 in a paper published in Zootaxa (volume 2165, pages 59–68) that simultaneously redescribed the closely related Betta anabatoides Bleeker. The type material was collected from the lower Kapuas basin in West Kalimantan, Indonesian Borneo. Eschmeyer's Catalog of Fishes (CAS) treats the valid name as Betta midas Tan, 2009; the authority is not parenthesised because the species was originally described in Betta, where it remains.
The species is placed in the anabatoides group, a cluster of large, robust mouthbrooding bettas centred on the island of Borneo. Tan (2009) distinguished B. midas from B. anabatoides primarily on morphometric grounds — B. midas is notably more slender relative to body depth — and on the distinctive golden iridescence of the opercle and lateral body scales that is absent or far less developed in B. anabatoides. Both species share the group's characteristic paternal mouthbrooding reproductive mode.
Morphology
Betta midas is a large betta, reaching 2.5 in standard length — substantial for the genus. The body is robust, with body depth measuring 24.3–29.0% of standard length, and the overall build is somewhat more slender than the stockier B. anabatoides. Fin counts are consistent with the group: one dorsal spine followed by 8–10 soft rays; one or two anal spines with 25–29 soft anal rays. Some median caudal rays project beyond the fin margin, giving the tail a slightly pointed appearance.
The most striking character is the live coloration. A broad black stripe runs from the lower lip through the eye and across the opercle; below and around that dark stripe, the opercle glows with bright gold iridescence. The body scales carry a similar gold to greenish-gold iridescent sheen across much of the flank. This combination — dark head stripe against gold opercular and body sheen — gives the fish a jewelled quality under good lighting, and directly inspired the species name.
Habitat
Betta midas occurs in the lower Kapuas basin of West Kalimantan, Indonesia, and in the Sambas river basin and the extreme western corner of Sarawak, Malaysia, in the Lundu area. Both regions lie in the lowland equatorial zone of Borneo, and the species has been collected from blackwater rivers running through or adjacent to peat swamp forest.
Peat swamp rivers are among the most chemically extreme freshwater habitats on earth. Organic acids leaching from the deep, waterlogged peat layers tint the water a deep amber to near-black, suppress pH to extremely low levels — FishBase records the lower range as 4.1 for this species — and keep dissolved oxygen low and conductivity near zero. The water is warm year-round, typically in the mid- to upper-20s Celsius, and flow is sluggish or still. These conditions suit the labyrinth organ of Betta: the suprabranchial air-breathing chamber allows the fish to gulp atmospheric oxygen at the surface, compensating for the oxygen-depleted water beneath. Betta midas is specifically a peat-swamp species, and this narrow habitat association is the core reason for its vulnerability.
Feeding
Like other members of the anabatoides group, Betta midas is a carnivore in the wild, taking invertebrates available in and around peat-swamp waterbodies. In the blackwater environment this primarily means insects — both aquatic larvae and terrestrial adults that fall onto the surface — along with small crustaceans and other small invertebrates.
In the aquarium the species accepts most meaty foods readily. Frozen and live foods such as bloodworm, Daphnia, brine shrimp, and mosquito larvae suit it well and should form the dietary core. High-quality dried foods may be accepted but should not be the sole offering; a diet with real variety maintains condition and colour. As a large, relatively solitary betta, it does not compete well at feeding in a community setting and is best managed in a species tank or with tankmates that do not outcompete it.
Mating
Betta midas is a paternal mouthbrooder, the reproductive mode shared by all members of the anabatoides group. Courtship follows the broad pattern typical of mouthbrooding bettas: the male displays to the female with spread fins and intensified coloration, and the pair circle and align for the spawning embrace. The male wraps around the female in the characteristic anabantoid embrace — the female curves into the male's body — and eggs and milt are released simultaneously as fertilisation occurs external to both parents.
After the embrace, the male collects the fertilised eggs in his mouth before the female can do so. Successive embraces may follow, with the male gathering more eggs each time, until the full clutch has been deposited and collected. At that point the female's role ends; the male retires to a secluded area of the tank and holds the eggs.
Breeding
Once the male has taken the egg mass into his buccal cavity he enters a period of incubation that typically lasts approximately one to two weeks for anabatoides-group species. During this time the male eats nothing and should not be disturbed. He tumbles and aerates the developing eggs with gentle movements of the mouth, and as they hatch he continues to hold the early larvae until the yolk sac is absorbed and the fry are free-swimming.
The male then releases the fry. Clutches in the anabatoides group are relatively small compared to bubble-nesting bettas — typically several dozen eggs — consistent with the greater parental investment required by buccal incubation. Once released, the fry are independent; the male does not feed them. At this point the male should be removed or the fry separated to prevent predation. The newly free-swimming fry are larger than those of bubble-nesting species and can generally take newly hatched brine shrimp from the outset, making early rearing comparatively straightforward.
In the aquarium
Betta midas is an infrequently encountered species in the hobby, available mainly through specialist wild-betta importers and dedicated breeders. Its requirements are the soft, warm, acidic conditions of its blackwater peat-swamp home: pH in the range of approximately 4–5 is ideal, though captive-bred individuals may tolerate somewhat higher values; temperature in the upper 20s Celsius; very soft water with negligible hardness; and subdued lighting with ample surface cover such as floating plants or leaf litter. Tannin-stained water replicated with Indian almond leaves or dried oak leaves closely mirrors natural conditions and appears to reduce stress.
Given its size — approaching 3 in — a pair requires a tank of at least 15 US gal, and more is better. Filtration should produce minimal current; a sponge filter is ideal. The labyrinth organ means the fish must have unobstructed access to the water surface, and the gap between the surface and the tank lid must be kept warm and humid to prevent chilling the organ. Betta midas is best kept as a pair or alone. It is likely to be aggressive toward conspecifics and may predate very small tankmates. During mouthbrooding the male should ideally be undisturbed; experienced keepers sometimes remove the female once egg collection is complete.
Conservation
The IUCN Red List assessed Betta midas as Vulnerable (VU) under criterion B1ab(iii) in December 2018, with the assessment published in 2019. The criterion reflects a restricted extent of occurrence combined with a projected continuing decline in the quality of occupied habitat. The assessor identified habitat loss from peat-swamp forest degradation and conversion across Borneo as the principal threat.
Peat swamp forest in Kalimantan and Sarawak has experienced severe and ongoing loss to drainage, plantation agriculture (particularly oil palm), logging, and fire. Because Betta midas is a peat-swamp specialist with a limited range centred on the lower Kapuas basin and a small sector of western Sarawak, it has no reservoir population in unaffected habitat to buffer local declines. Captive breeding by specialist hobbyists contributes to ex-situ security, but the long-term outlook for the species depends on the fate of remaining intact peat-swamp ecosystems in western Borneo.